<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title></title>
    <style media="screen">
      div {width:200px; height:200px; background:#CCC; float:left; margin:10px;}
    </style>
    <script>
    window.onload=function (){
      let aDiv=document.getElementsByTagName('div');

      Array.from(aDiv).forEach(div=>{
        div.style.background='yellow';
      });
    };
    </script>
  </head>
  <body>
    <div class=""></div>
    <div class=""></div>
    <div class=""></div>
    <div class=""></div>
    <div class=""></div>
  </body>
</html>
